01 - Preheat oven to 350°F. Line a 9×9-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - Combine graham cracker crumbs, granulated sugar, and melted butter in a medium bowl, stirring until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 8 minutes, then set aside to cool slightly.
03 - Using an electric mixer, beat the softened cream cheese and granulated sugar together in a large bowl until completely smooth and free of lumps. Add the eggs one at a time, beating well after each addition. Blend in the vanilla extract and sour cream until just incorporated — avoid overmixing.
04 - Pour the cheesecake filling over the baked crust, using a spatula to spread it into a smooth, even layer.
05 - Toss the diced peaches with granulated sugar and lemon juice in a separate bowl until evenly coated. Distribute the peach pieces across the cheesecake surface and gently press them partway into the batter.
06 - Bake for 30 to 32 minutes, until the edges are lightly golden and the center is just set with a slight jiggle remaining. Remove from the oven and allow to cool completely at room temperature.
07 - Once cooled to room temperature, transfer the pan to the refrigerator and chill for at least 2 hours, or until the cheesecake is firm and fully set.
08 - Beat the heavy whipping cream with powdered sugar using an electric mixer until soft peaks form. Be careful not to overwhip.
09 - Lift the chilled cheesecake slab from the pan using the parchment paper overhang. Slice into 12 even bars and top each with a dollop of whipped cream before serving.